Concrete batching pre-mixer and method

Abstract

A pre-mixer agglomerator and method of pre-mixing batching ingredients used to produce concrete mixes is disclosed. Specifically, this invention involves a pre-mix system which blends the wetting agents and the cementitious ingredients in relation to each other at any selected ratio in an adjustable and repeatable manner. The pre-mixer is a twin screw, preferably counter-rotating, pre-mixer agglomerator unit for pre-mixing these materials prior to combining them with aggregates in a drum of a transit mixer truck or other final mixing vessel.

1 . An agglomerator apparatus for blending free-flowing dry materials and wetting agents for use in the preparation of batches of mixed concrete in a concrete batching process comprising: 
 (a) a mixing chamber for receiving and processing dry materials to be mixed and combined with one or more liquid wetting agents, said chamber having at least a first inlet opening and a discharge opening, said first inlet opening, and said discharge opening being located toward opposite ends thereof;    (b) a twin screw mixer including a pair of spaced generally parallel screw conveyors disposed in intermeshing relation designed for rotation and having flights characterized by a sequence of different pitches therealong, including inlet metering, mixing, and discharging section pitches, mounted in said mixing chamber for conveying, mixing and discharging materials received in said mixing chamber, and thereby characterizing said mixing chamber as having inlet, mixing and discharge sections, respectively;    (c) a liquid supply system including inlets for supplying metered amounts of liquid wetting agents to selected portions of said mixing chamber for blending with said dry materials; and    (d) drive arrangement for rotating said pair of mixing screw conveyors in a coordinated manner.    
   
   
       2 . An apparatus as in  claim 1  wherein said twin screw mixer includes screw conveyors designed for counter-rotation.  
   
   
       3 . An agglomeration apparatus as in  claim 2  wherein said counter-rotation directs material away from said liquid supply system inlets.  
   
   
       4 . An apparatus as in  claim 1  wherein said screw includes a pair of parallel screw conveyors designed for rotation in the same direction.  
   
   
       5 . An apparatus as in  claim 1  wherein said liquid supply system further comprises a liquid supply source for applying said liquid wetting agents to said mixing chamber from a plurality of spaced locations in said mixing section.  
   
   
       6 . An agglomerator apparatus as in  claim 1  wherein said one or more wetting agents includes a major fraction of water.  
   
   
       7 . An agglomerator apparatus as in  claim 1  wherein said dry materials are cementitious ingredients.  
   
   
       8 . An apparatus as in  claim 1  wherein each of said pair of spaced intermeshing mixing screw conveyors are characterized by shaped flights fixed to a central shaft in a manner that thereby forms in effect a continuous helix.  
   
   
       9 . An apparatus as in  claim 1  wherein each of said pair of intermeshing mixing screw conveyors comprises shaped flights fixed to a hollow tubular member which, in turn, is mounted to rotate with a central shaft in a manner that allows removal of said tube from said central shaft.  
   
   
       10 . An apparatus as in  claim 1  wherein said agglomerator is adapted to receive dry materials into said metering inlet section of said mixing chamber from a screw conveyor pre-feeder.  
   
   
       11 . An apparatus as in  claim 1  wherein said mixing chamber further comprises an inlet opening above said discharge opening to allow dry material to by-pass said mixing chamber.  
   
   
       12 . An apparatus as in  claim 1  further comprising a device for supplying dry materials into said metering inlet section of said mixing chamber.  
   
   
       13 . An apparatus as in  claim 1  wherein said intermeshing screw conveyors of said twin screw mixer are characterized by said inlet metering section having a narrow pitch, said mixing section having a pitch greater than that of the inlet metering section and said discharge section having a pitch greater than that of the mixing section.  
   
   
       14 . An apparatus as in  claim 13  wherein said inlet metering section of said intermeshing mixing screw conveyors is characterized by a pitch equal to about one-half pitch or less.  
   
   
       15 . An apparatus as in  claim 1  wherein said inlet metering section of said intermeshing mixing screw conveyors is characterized by a pitch equal to about one-half pitch or less.  
   
   
       16 . An apparatus as in  claim 1  wherein said mixing section of said intermeshing mixing screw conveyors is characterized by a pitch equal to about one full pitch or less.  
   
   
       17 . An apparatus as in  claim 14  wherein said mixing section of said intermeshing mixing screw conveyors is characterized by a pitch equal to about one full pitch or less.  
   
   
       18 . An apparatus as in  claim 1  wherein said discharge section of said intermeshing mixing screw conveyors is characterized by paddles or scoops.  
   
   
       19 . An apparatus as in  claim 17  wherein said discharge section of said intermeshing mixing screw conveyors is characterized by paddles or scoops.  
   
   
       20 . An apparatus as in  claim 1  wherein each of said pair of spaced intermeshing mixing screw conveyors comprises a plurality of consecutive removable flight segments keyed to a main shaft.  
   
   
       21 . An apparatus as in  claim 20  wherein each of said flight segments comprises a pitched hub having an offset step surrounded by disk having angled cutouts.  
   
   
       22 . An apparatus as in  claim 21  wherein said shafts carrying said flight segments are rotationally offset by 45°.  
   
   
       23 . An apparatus as in  claim 20  wherein said shafts are not round and said hubs of said screw flights are provided with central hub cutouts having the same shape as said shafts which are designed to slip over the shafts in assembling each conveyor.  
   
   
       24 . An apparatus as in  claim 21  wherein said shafts are not round and said hubs of said screw flights are provided with central hub cutouts having the same shape as said shafts which are designed to slip over the shafts in assembling each conveyor.  
   
   
       25 . An apparatus as in  claim 1  further comprising a programmable control system for controlling the operation of said agglomerator and the preparation of a batch of mixed concrete, said control system further including: 
 (a) a liquid wetting agent flow control valve for controlling the rate of distribution of liquid wetting agent to said mixing chamber;    (b) a meter for monitoring both the total amount of liquid wetting agent and the rate of which the liquid wetting agent is delivered to the agglomerator during the mixing of dry ingredients; and    (c) a dry ingredient flow control device for controlling the rate and total amount of dry ingredients fed to the inlet of the agglomerator.    
   
   
       26 . An apparatus as in  claim 18  wherein said discharge section of said intermeshing mixing screw conveyors is characterized by a paddle construction.  
   
   
       27 . An apparatus as in  claim 19  wherein said discharge section of said intermeshing mixing screw conveyors is characterized by a paddle construction.  
   
   
       28 . An apparatus as in  claim 18  wherein said discharge section of said intermeshing mixing screw conveyors is characterized by a scoop-shaped flat pitch.  
   
   
       29 . An apparatus as in  claim 19  wherein said discharge section of said intermeshing mixing screw conveyors is characterized by a scoop-shaped flat pitch.  
   
   
       30 . An apparatus as in  claim 1  wherein said screw conveyors include metal flights.  
   
   
       31 . An apparatus as in  claim 1  wherein said screw conveyors include metal flights coated with a non-metallic material.  
   
   
       32 . An apparatus as in  claim 31  wherein said non-metallic material includes a polyamide.  
   
   
       33 . An apparatus as in  claim 31  wherein said non-metallic material includes a nylon.  
   
   
       34 . An apparatus as in  claim 31  wherein said non-metallic material includes a polyurethane.  
   
   
       35 . An apparatus as in  claim 1  wherein said screw conveyors include non-metallic flights.  
   
   
       36 . An apparatus as in  claim 1  wherein said screw conveyors include an amount of a non-metallic composite material.  
   
   
       37 . An agglomeration apparatus for blending finely divided free-flowing dry materials and wetting agents for use in the preparation of batches of mixed concrete in a concrete batching process comprising: 
 (a) a mixing chamber for receiving and processing one or more dry materials to be mixed and combined with one or more liquid wetting agents, said chamber having at least a first inlet opening and a discharge opening, said first inlet opening, and said discharge opening being located toward opposite ends thereof;    (b) a twin screw mixer including a pair of spaced generally parallel screw conveyors disposed for counter rotation in intermeshing relation and having flights characterized by a sequence of different pitches therealong, including inlet metering, mixing, and discharging section pitches, mounted in said mixing chamber for conveying, mixing and discharging materials received in said mixing chamber;    (c) a liquid supply system including a pattern of inlets in said mixing chamber for supplying metered amounts of liquid wetting agents to selected portions of said mixing chamber for agglomerating said dry materials to form relatively free-flowing bead-like particulates; and    (d) drive arrangement for rotating said pair of mixing screw conveyors.    
   
   
       38 . An apparatus as in  claim 37  further comprising a device for metering dry materials into said metering inlet section of said mixing chamber.  
   
   
       39 . An apparatus as in  claim 37  wherein said intermeshing screw conveyors of said twin screw mixer are characterized by said inlet metering section having a narrow pitch, said mixing section having a pitch greater than that of the inlet metering section and said discharge section having a pitch greater than that of the mixing section.  
   
   
       40 . An apparatus as in  claim 37  wherein said screw conveyors are designed to pull material away from said inlets.  
   
   
       41 . A method of preparing a pre-mix of cementitious ingredients and wetting agents including steps of: 
 (a) metering selected total amounts of dry cementitious ingredients at a selected rate into an inlet section of an operating pre-mixer agglomerator, said agglomerator further being characterized by a twin screw mixer including a pair of screw conveyors, spaced in generally parallel intermeshing relation and having flights characterized by a plurality of different pitches therealong and including a relatively narrow pitch inlet metering section, a broader pitch mixing section and a discharge section having a still broader pitch;    (b) combining said dry materials with a selectively controlled amount of wetting agents, including water, supplied at a predetermined rate at selected intervals along said mixing section;    (c) discharging said pre-mix into a final mixing vessel; and    (d) adding aggregate and any additional wetting agents required to bring the mix to the desired consistency in said final mixing vessel.    
   
   
       42 . A method according to  claim 41  wherein said additional water is also added via said twin screw mixing conveyor.  
   
   
       43 . A method as in  claim 41  wherein said finely divided dry material is metered into said agglomerate mixing vessel by a narrow pitch screw conveyor pre-feeder.  
   
   
       44 . A method as in  claim 41  wherein said final mixing vessel is a drum mounted on a mobile concrete mixing vehicle.  
   
   
       45 . A method as in  claim 41  wherein said pair of screw conveyors are driven in counter-rotating fashion.  
   
   
       46 . A method as in  claim 45  wherein said pair of screw conveyors are rotated so as to pull material being mixed away from sources of agglomerating liquid.  
   
   
       47 . A method as in  claim 41  wherein said agglomerating liquid is primarily water and is added in an amount in the range of about 0.1:1 to about 0.25:1 by weight.